A conjugated diene such as 1,3-butadiene or isoprene is generally isolated and purified from a hydrocarbon mixture containing the conjugated diene, such as a C4 hydrocarbon mixture or C5 hydrocarbon mixture by a series of distilling operations, particularly extractive distillations. The problems of polymer formation can occur in extractive distillations, which can clog distillation equipments, for example, distillation columns, heat exchangers, reflux condensers, and evaporators. The polymer clogging problem causes frequent shut-downs of the operation so the polymer can be cleaned from the operating unit.
U.S. Pat. No. 6,395,953 teaches a process for preparing a purified conjugated diene by extractive distillation with an extraction solvent comprising an amide compound and 0.01 to 10 weight percent of a heterocyclic aldehyde. However, the polymer clogging problem still occurs during the distillation when such an extraction solvent is used. This invention is to reduce or prevent polymer clogging of distillation equipment during the extractive distillation of a conjugated diene from a hydrocarbon mixture.